<div>
  Delegates the groups resolution to a custom script.
  
  <p>
  Each time the authentication is attemped (which is once per session),
  the specified script will be invoked with the username in the 'U' environment variable.
  If the script returns exit code 0, the output will be tokenized by the delimiter (default: ',')
  to create a group with each token.

  <p>
  In case of the failure, the output from the process will be reported in the exception message.
</div>